Compositions of hypochlorous acid and methods of manufacture thereof

ABSTRACT

The invention generally relates to compositions of hypochlorous acid (HOCl) and methods of manufacture thereof. In certain aspects, the invention provides air-free compositions of HOCl. In other aspects, the invention provides methods of making HOCl that involve mixing together in water in an air-free environment, a compound that generates a proton (H+) in water and a compound that generates a hypochlorite anion (OCl−) in water to thereby produce air-free hypochlorous acid.

RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 16/795,000, filed Feb. 19, 2020, which is a continuation ofU.S. patent application Ser. No. 14/618,799, filed Feb. 10, 2015 (issuedas U.S. Pat. No. 10,577,244), which is a continuation of U.S. patentapplication Ser. No. 13/770,738, filed Feb. 19, 2013 (issued as U.S.Pat. No. 9,492,479), which claims priority to and the benefit of U.S.provisional application Ser. No. 61/600,344, filed Feb. 17, 2012, thecontent of each of which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The invention generally relates to compositions of hypochlorous acid(HOCl) and methods of manufacture thereof.

BACKGROUND

Hypochlorous acid (HOCl) is a weak acid that is known to rapidlyinactivate bacteria, algae, fungus, and other organics, making it aneffective agent across a broad range of microorganisms. Additionally,since hypochlorous acid is a weak acid and since people naturallyproduce certain compounds that allow them to tolerate hypochlorous acid(e.g., the amino acid taurin), it is generally not harmful to people.Due to the combination of its biocide properties and its safety profile,hypochlorous acid has been found to have many beneficial uses acrossmany different industries, such as the medical, foodservice, foodretail, agricultural, wound care, laboratory, hospitality, dental, orfloral industries.

Hypochlorous acid is formed when chlorine dissolves in water. Onemanufacturing method involves the electrochemical activation of asaturated salt solution (e.g., brine) to form HOCl. Another productionmethod involves the disproportionation of chlorine gas in alkalinesolutions.

A problem with hypochlorous acid produced by these methods is that it ishighly unstable, and over a short period of time (e.g., a few hours to acouple of weeks) the hypochlorous acid will degrade. The distribution ofchloric compounds in aqueous solution is known to be a function of pH.As the pH of a solution containing hypochlorous acid becomes more acidic(e.g., pH below 3), chlorine gas is formed. As the pH of a solutioncontaining hypochlorous acid becomes more basic (e.g., pH above 8)hypochlorite anions (OCl—; i.e., bleach) are formed, which are alsotoxic to people. Thus, while being an effective biocide, the use ofhypochlorous acid has been limited by the need for onsite generation andthe challenge of maintaining storage stability.

SUMMARY

The invention recognizes that aspects of the production process formaking hypochlorous acid (HOCl) may contribute to the instability of theproduct. Particularly acidic pH, due to donation of a proton from anacid in the reaction, causes instability in the HOCl composition.Additionally, exposure to air during the production process has beenshown to destabilize the HOCl, which destabilization process canescalate quickly. Methods of the invention provide air-free mixingmethods for producing hypochlorous acid that do not rely on electrolysisor use of chlorine gas. Methods of the invention produce an air-free,stable formulation of hypochlorous acid that can be bottled and storedfor a significant period of time (e.g., from at least a couple of monthsto 6 to 12 months or longer), eliminating the need for onsite generationand overcoming the challenges of maintaining storage stability.

In certain aspects, methods of the invention involve mixing together inwater in an air-free environment, a compound that generates a proton(H⁺) in water and a compound that generates a hypochlorite anion (OCl⁻)in water to thereby produce air-free hypochlorous acid. Any compoundthat produces a hypochlorite anion (OCl⁻) in water may be used withmethods of the invention. Exemplary compounds include NaOCl, Ca(OCl)₂,and Mg(OCl)₂. In particular embodiments, the compound is NaOCl. Anycompound that produces a proton (H⁺) in water may be used with methodsof the invention. Preferred compounds are acids, such as acetic acid(CH₃CO₂H), HCl and H₂SO₄. Methods of the invention result in theproduction of a highly-pure and stable HOCl composition with mildbuffering capacity (e.g., pH 3.6-5.6 for acetic acid and 6.5-8.5 forHCl). Stability is increased at the lower pH, so low pH buffers arepreferred.

Methods of the invention include introducing to water a compound thatgenerates a proton and a compound that generates a hypochlorite anion inany order (e.g., simultaneously or sequentially) and in any manner(aqueous form, solid form, etc.). For example, the compound thatgenerates a proton and the compound that generates the hypochloriteanion are each aqueous solutions and are introduced to the watersequentially, e.g., the compound that generates the proton may beintroduced to the water first and the compound that generates thehypochlorite anion may be introduced to the water second. However,methods of the invention include other orders for sequentialintroduction of the compound that generates the proton and the compoundthat generates the hypochlorite anion.

Methods of the invention may be conducted with most types of water,including tap water. In certain embodiments, the water is filtered orpurified water, such as that obtained from any water purificationcompany, such as Millipore (Billerica, Mass.). In certain embodiments,the water has a buffering capacity from about pH 6 to about pH 8. Incertain embodiments, the water has a buffering capacity from about pH3.6 to about pH 6, but in any case not low enough to produce Cl₂ gases.In other embodiments, the water is deionized water to which at least onebuffering agent has been added, such as acetic buffer or phosphatebuffer. In particular embodiments, an initial pH of the water prior toaddition of the acetic acid, HCl or the compound that generates thehypochlorite anion is at least about 8, (e.g., 8.1 or greater, 8.2 orgreater, 8.3 or greater, 8.4 or greater, 8.5 or greater, 8.6 or greater,8.7 or greater, 8.8 or greater, 8.9 or greater, 9.0 or greater, 9.5 orgreater, 10.0 or greater, 10.5 or greater, or 10.8 or greater). Inspecific embodiments, the pH of the water prior to addition of eitherthe compound that generates the proton or the compound that generatesthe hypochlorite anion is 8.4. In certain embodiments, NaOH isintroduced at the beginning of the process to enhance the bufferingproperties of the final solution.

Generally, the reagents are added to the water in relatively smallamounts compared to the flow of water. In certain embodiments, no morethan about 0.6 mL amount of the compound that generates the proton isintroduced to the water at a single point in time. In other embodiments,no more than about 0.6 mL amount of the compound that generates thehypochlorite anion is introduced to the water at a single point in time.

Generally, the added reagents are turbulently mixed. Such turbulentmixing may be accomplished by using a mixing device that is configuredto produce a plurality of vortexes within a mixing chamber. In certainembodiments, the compound that generates the proton is introduced to thewater and turbulently mixed with the water prior to the introduction tothe water of the compound that generates the hypochlorite anion. Then,the compound that generates the hypochlorite anion is introduced to thewater after the compound that generates the proton has been turbulentlymixed with the water, and after introduction, the compound thatgenerates the hypochlorite anion is turbulently mixed with the water.

Methods of the invention can be conducted in any type of vessel orchamber or fluidic system. For example, a fluidic system including pipesand mixing devices is used to conduct methods of the invention. In suchembodiments, the water is flowing through a pipe, and the reagents (e.g,the compound that generates the proton and the compound that generatesthe hypochlorite anion) are introduced to the water as it is flowingthrough the pipe. The mixing devices are in-line with the piping system.Generally, the water in the pipe is flowing at a rate from about 0.1liters per second to about 1 liter per second and is under a pressure ofat least about 0.1 bar, such as for example 1 bar or greater. In certainembodiments, the method is performed under pressure. In certainembodiments, the method is performed in an air-free environment andunder pressure. Methods of the invention may be performed manually or inan automated fashion.

Another aspect of the invention provides methods that involve mixingtogether in water, a compound that generates a proton (H⁺) and acompound that generates a hypochlorite anion (OCl⁻) in water to therebyproduce hypochlorous acid, in which the method is performed without useof chlorine gas or use of electrolysis.

Another aspect of the invention provides methods that involveturbulently mixing together in water, a compound that generates a proton(H⁺) and a compound that generates a hypochlorite anion (OCl⁻) in waterto thereby produce hypochlorous acid.

Another aspect of the invention provides methods that involveintroducing hydrochloric acid (HCl) to a flow of water having a pH fromabout 8 to about 9, turbulently mixing the HCl with the flowing water ina first mixing device, introducing sodium hypochlorite (NaOCl) to thewater after the water has exited the first mixing device, andturbulently mixing the NaOCl with the flowing water in a second mixingdevice, thereby producing hypochlorous acid (HOCl), in which the methodis performed in an air-free environment and under pressure.

Methods of the invention produce an air-free composition of hypochlorousacid (HOCl). In certain embodiments, the composition is substantiallyfree of chlorine gas. The composition may have a pH from about 4 toabout 7.5, more particularly, from about 6.0 to about 7.0. The HOCl mayhave a concentration of at least about 200 ppm. Compositions of theinvention are stable and storable for long periods of time, e.g., fromabout 1 month to about 1 year.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing an exemplary system for producinghypochlorous acid according to methods of the invention.

FIG. 2 is a schematic showing a magnified view of the mixing deviceshown in FIG. 1 .

FIG. 3 is a schematic showing an internal view of the mixing chamber ofthe mixing device.

FIG. 4 is a schematic showing a front view of the members that dividethe mixing chamber into a plurality of sub-chambers. This view shows theapertures in the members.

FIG. 5 is a schematic showing a valve configured with measuring sensorsfor switching from a waste line to a product collection line.

FIG. 6 is a schematic showing the valve in-line with the waste line andthe product collection line.

FIG. 7 is a schematic showing another exemplary system for producinghypochlorous acid according to methods of the invention. This system isconfigured for automated use with buffered deionized water. The buffercan either be included in the inflowing water or can be introducedthrough an injection port. The buffer may also be mixed during themixing process by using NaOH in NaOCl or separately injected and aceticacid or others similar acids or bases.

FIG. 8 is a graph of a calibration curve showing HOCl concentration(ppm) calculated indirectly versus conductivity.

FIG. 9 is a graph showing a spectrophotometric analysis of the producedHOCl. The gases generally produced during production of HOCl are ClO₂,Cl₂O and Cl₂, all of which are detectable in the visible range as yellowor yellow-red. The graph shows no absorption from colored gases in theproduced HOCl.

FIG. 10 is a graph showing the amount (parts per million (ppm)) of HOClinitially produced (T=0) and its stability over time.

FIG. 11 is a graph showing how the pH of the HOCl product changed overtime.

FIG. 12 is a graph showing the oxidation and reduction (redox) of theHOCl product over time.

DETAILED DESCRIPTION

The basis of compositions and methods of the invention is theprotonation of the hypochlorite ion (OCl⁻). Using HCl and NaOCl as anexample, the protonation is accomplished by introducing an acid (e.g.,HCl) to the solution, which results in the following reaction occurring:

HCl_((aq))+NaOCl_((aq))↔HOCl_((aq))+NaCl_((aq)).

The hypochlorous acid in aqueous solution partially dissociates into theanion hypochlorite (OCl⁻), thus in aqueous solution there is always anequilibrium between the hypochlorous acid and the anion (OCl⁻). Thisequilibrium is pH dependent and at higher pH the anion dominates. Inaqueous solution, hypochlorous acid, is also in equilibrium with otherchlorine species, in particular chlorine gas, Cl₂, and various chlorineoxides. At acidic pH, chlorine gases become increasingly dominant whileat neutral pH the different equilibria result in a solution dominated byhypochlorous acid. Thus, it is important to control exposure to air andpH in the production of hypochlorous acid.

Additionally, the concentration of protons (H⁺) affects the stability ofthe product. The invention recognizes that the proton concentration canbe controlled by using an acid that has a lesser ability at a given pHto donate a proton (i.e., the acid can provide buffering capacity). Forexample, conducting the process with acetic acid instead of hydrochloricacid is optimal when the desired pH of the final solution isapproximately the pKa of acetic acid. This can be achieved by mixingratios in water of 250× or greater, meaning 1 part proton donor at 100%concentration (e.g., HCl or acetic acid) to 250 parts water.

The invention generally relates to methods of producing hypochlorousacid (HOCl). In certain embodiments, methods of the invention involvemixing together in water in an air-free environment, a compound thatgenerates a proton (H⁺) in water and a compound that generates ahypochlorite anion (OCl⁻) in water to thereby produce air-freehypochlorous acid. The water may be tap water or purified water, such aswater purchased from a water purification company, such as Millipore(Billerica, Mass.). Generally, the pH of the water is maintained fromabout 4.5 to about 9 during the method, however the pH may go above andbelow this range during the production process. Conducting methods ofthe invention in an air-free environment prevents the build-up ofchlorine gases during the production process. Further, conductingmethods of the invention in an air-free environment further stabilizesthe produced HOCl.

Any compound that produces a hypochlorite anion (OCl⁻) in water may beused with methods of the invention. Exemplary compounds include NaOCland Ca(OCl)₂. In particular embodiments, the compound is NaOCl. Anycompound that produces a proton (H⁺) in water may be used with methodsof the invention. Exemplary compounds are acids, such as acetic acid,HCl and H₂SO₄. In particular embodiments, the compound is HCl. Inpreferred embodiments, the compound is acetic acid because it is aweaker acid with a preferred pKa to HCl, meaning, it donates lessprotons during the reaction than HCl and able to maintain the preferredpH level better.

Methods of the invention can be conducted in any type of vessel orchamber or fluidic system. In certain embodiments, a fluidic system 100as shown in FIG. 1 is used to perform methods of the invention. Thesystem 100 includes a series of interconnected pipes 101 a-c with aplurality of mixing devices 102 and 103 in-line with the plurality ofpipes 101 a-c. The pipes and the mixing devices can be interconnectedusing seals such that all air can be purged from the system, allowingfor methods of the invention to be performed in an air-free environment.In certain embodiments, methods of the invention are also conductedunder pressure. Conducting methods of the invention in an air-freeenvironment and under pressure allows for the production of HOCl thatdoes not interact with gases in the air (e.g., oxygen) that maydestabilize the produced HOCl.

Pipes 101 a-c generally have an inner diameter that ranges from about 5mm to about 50 mm, more preferably from about 17 mm to about 21 mm. Inspecific embodiments, the pipes 101 a-c have an inner diameter of about21 mm. Pipes 101 a-c generally have a length from about 10 cm to about400 cm, more preferably from about 15 cm to about 350 cm. In certainembodiments, pipes 101 a-c have the same length. In other embodiments,pipes 101 a-c have different lengths. In specific embodiments, pipe 101a has a length of about 105 cm, pipe 101 b has a length of about 40 cm,and pipe 101 c has a length of about 200 cm.

The pipes and mixers can be made from any inert material such thatmaterial from the pipes and mixers does not become involved with thereaction occurring within the fluidic system. Exemplary materialsinclude PVC-U. Pipes are commercially available from Georg Ficher AB.The pipes and mixers can be configured to have a linear arrangement suchthat the pipes and the mixers are arranged in a straight line.Alternatively, the pipes and mixers can have a non-linear arrangement,such that the water must flow through bends and curves throughout theprocess. System 100 shows a non-linear configuration of the pipes 101a-c and mixers 102 and 103.

Pipe 101 a is an inlet pipe that receives the water that will flowthrough the system. Generally, the water in pipes 101 a-c is under apressure of at least about 0.1 bar, such as for example, 0.2 bar orgreater, 0.3 bar or greater, 0.4 bar or greater, 0.5 bar or greater, 0.7bar or greater, 0.9 bar or greater, 1.0 bar or greater, 1.2 bar orgreater, 1.3 bar or greater, or 1.5 bar or greater. At such pressures, aturbulent water flow is produced, thus the reagents are introduced to ahighly turbulent water flow which facilitates an initial mixing of thereagents with the water prior to further mixing in the mixing devices102 and 103.

In order to control the pH during the production process, the incomingwater should have a buffering capacity in the range of pH 3.5-9.0, morepreferably from 6.0 and 8.0, to facilitate addition of the compoundsthat generates the proton and the compound that generates thehypochlorite anion. The dissolved salts and other molecules found inmost tap waters gives the tap water a buffering capacity in the range ofpH 5.5-9.0, and thus tap water is a suitable water to be used withmethods of the invention.

In certain embodiments, deionized water with the addition of knownbuffering agents to produce a water having a buffering capacity in therange of pH 3.5-9.0 is used. On example of a buffer in this particularrange is phosphate buffer. For greater process control and consistency,using a formulated deionized water may be preferable to using tap waterbecause tap water can change between locations and also over time.Additionally, using deionized water with known additives also ensures astable pH of the incoming water flow. This process is discussed ingreater detail below.

In particular embodiments, an initial pH of the water prior to additionof either the compounds that generates the proton or the compound thatgenerates the hypochlorite anion is at least about 8.0, including 8.1 orgreater, 8.2 or greater, 8.3 or greater, 8.4 or greater, 8.5 or greater,8.6 or greater, 8.7 or greater, 8.8 or greater, 8.9 or greater, 9.0 orgreater, 9.5 or greater, 10.0 or greater, 10.5 or greater, or 10.8 orgreater. In specific embodiments, the pH of the water prior to additionof either the compound that generates the proton or the compound thatgenerates the hypochlorite anion is 8.4.

Methods of the invention include introducing to the water the compoundthat generates the proton and the compound that generates thehypochlorite anion in any order (e.g., simultaneously or sequentially)and in any manner (aqueous form, solid form, etc.). For example, thecompound that generates the proton and the compound that generates thehypochlorite anion are each aqueous solutions and are introduced to thewater sequentially, e.g., the compound that generates the proton may beintroduced to the water first and the compound that generates thehypochlorite anion may be introduced to the water second. However,methods of the invention include other orders for sequentialintroduction of the compound that generates the proton and the compoundthat generates the hypochlorite anion.

System 100 is configured for sequential introduction of reagents to thewater flow, and the process is described herein in which the compoundthat generates the proton is introduced to the water first and thecompound that generates the hypochlorite anion is introduced to thewater second. In certain embodiments, the compound that generates theproton and the compound that generates the hypochlorite anion areintroduced to the water in small aliquots, e.g, from about 0.1 mL toabout 0.6 mL. The iterative and minute titrations make it possible tocontrol the pH in spite of additions of acid (compound that generatesthe proton) and alkali (the compound that generates the hypochloriteanion). In certain embodiments, no more than about 0.6 mL amount ofcompound that generates the proton is introduced to the water at asingle point in time. In other embodiments, no more than about 0.6 mLamount of the compound that generates the hypochlorite anion isintroduced to the water at a single point in time.

To introduce the reagents to the water, pipe 101 a includes an injectionport 104 and pipe 101 b includes an injection port 105. The injectionports 104 and 105 allow for the introduction of reagents to the waterflow. In this embodiments, aqueous compound that generates the proton isintroduced to the water in pipe 101 a via injection port 104. Thecompound that generates the proton is introduced by an infusion pumpthat is sealably connected to port 104. In this manner, the flow rate,and thus the amount, of compound that generates the proton introduced tothe water at any given time is controlled. The infusion pump can becontrolled automatically or manually. The rate of introduction of thecompound that generates the proton to the water is based upon theincoming water quality (conductivity and pH level) and the pressure andthe flow of the incoming water. In certain embodiments, the pump isconfigured to introduce about 6.5 liters per hour of hydrochloric acidinto the water. The introducing can be a continuous infusion or in anintermittent manner. Since the water is flowing though the pipes in aturbulent manner, there is an initial mixing of the compound thatgenerates the proton with the water upon introduction of thehydrochloric acid to the water.

Further mixing occurs when the water enters the first mixing device 102.FIG. 2 shows a magnified view of the mixing device 102 shown in FIG. 1 .In the illustrated embodiment, the mixing device includes a length ofabout 5.5 cm and a diameter of about 5 cm. One of skill in the art willrecognize that these are exemplary dimensions and methods of theinvention can be conducted with mixing devices having differentdimensions than the exemplified dimensions. Mixing device 102 includes afluidic inlet 106 that sealably couples to pipe 101 a and a fluidicoutlet 107 that sealably couples to pipe 101 b. In this manner, watercan enter the mixing chamber 108 of device 102 from pipe 101 a and exitthe chamber 108 of device 102 through pipe 101 b.

The mixing device 102 is configured to produce a plurality of fluidicvortexes within the device. An exemplary device configured in such amanner is shown in FIG. 3 , which is a figure providing an internal viewof the chamber 108 of device 102. The chamber 108 includes a pluralityof members 109, the members being spaced apart and fixed within thechamber 108 perpendicular to the inlet and the outlet in order to form aplurality of sub-chambers 110. Each member 109 includes at least oneaperture 111 that allows fluid to flow there through. FIG. 4 shows afront view of the members 109 so that apertures 111 can be seen. Thesize of the apertures will depend on the flow of water and the pressurein the system.

Any number of members 109 may be fixed in the chamber 108, the number ofmembers 109 fixed in the chamber 108 will depend on the amount of mixingdesired. FIG. 4 shows four members 109 a-d that are fixed in the chamberto produce four sub-chambers 110 a-d. The members 109 may be spacedapart a uniform distance within the chamber 108, producing sub-chambers110 of uniform size. Alternatively, the members 109 may be spaced apartat different distances within the chamber 108, producing sub-chambers110 of different size. The members 109 are of a size such that they maybe fixed to an interior wall within the chamber 108. In this manner,water cannot flow around the members and can only pass through theapertures 111 in each member 109 to move through mixing device 102.Generally, the members will have a diameter from about 1 cm to about 10cm. In specific embodiments, the members have a diameter of about 3.5cm.

A fluidic vortex is produced within each sub-chamber 110 a-d. Thevortices result from flow of the water through the apertures 111 in eachmember 109. Methods of the invention allow for any arrangement of theapertures 111 about each member 109. FIG. 4 illustrates non-limitingexamples of different arrangements of the apertures 111 within a member109. The apertures may be of any shape. FIG. 4 illustrates circularapertures 111. In certain embodiments, all of the apertures 111 arelocated within the same place of the members 109. In other embodiments,the apertures 111 are located within different places of the members109. Within a single member 109, all of the apertures 111 may have thesame diameter. Alternatively, within a single member 110, at least twoof the apertures 111 have different sizes. In other embodiments, all ofthe apertures 111 within a single member 110 have different sizes.

In certain embodiments, apertures 111 in a member 110 have a first sizeand apertures 111 in a different member 110 have a different secondsize. In other embodiments, apertures 111 in at least two differentmembers 110 have the same size. The size of the apertures will depend onthe flow of water and the pressure in the system. Exemplary aperturediameters are from about 1 mm to about 1 cm. In specific embodiments,the apertures have a diameter of about 6 mm.

The solution enters mixing device 102 through inlet 106, which issealably mated with pipe 101 a. The solution enters the chamber 108 andturbulent mixing occurs in each of sub-chambers 110 a-d as the solutionpass through members 109 a-d via the apertures 111 in each member 109a-d. After mixing in the final sub-chamber 110 d, the water exits thechamber 108 via the fluidic outlet 107 which is sealably mated to pipe101 b.

The compound that generates the hypochlorite anion is next introduced tothe solution that is flowing through pipe 101 b via injection port 105.The compound that generates the hypochlorite anion is introduced by aninfusion pump that is sealably connected to port 105. In this manner,the flow rate, and thus the amount, of compound that generates thehypochlorite anion introduced to the water at any given time iscontrolled. The infusion pump can be controlled automatically ormanually. The rate of introduction of the compound that generates thehypochlorite anion to the water is based upon properties of the solution(conductivity and pH level) and the pressure and the flow of thesolution. In certain embodiments, the pump is configured to introduceabout 6.5 liters per hour of compound that generates the hypochloriteanion into the solution. The introducing can be a continuous infusion orin an intermittent manner. Since the solution is flowing though thepipes in a turbulent manner, there is an initial mixing of the compoundthat generates the hypochlorite anion with the solution uponintroduction of the compound that generates the hypochlorite anion tothe solution.

Further mixing occurs when the solution enters the second mixing device103. Mixing device 103 includes all of the features discussed above withrespect to mixing device 102. Mixing device 103 may be configured thesame or differently than mixing device 102, e.g., same or differentnumber of sub-chambers, same or different diameter of apertures, same ordifferent sizes of sub-chambers, etc. However, like mixing device 102,mixing device 103 is configured to produce a fluidic vortex within eachsub-chamber.

The solution enters mixing device 103 through an inlet in the device,which is sealably mated with pipe 101 b. The solution enters the mixingchamber and turbulent mixing occurs in each sub-chamber of the mixingdevice as the solution pass through members in the chamber via theapertures in each member. After mixing in the final sub-chamber, thewater exits the chamber via the fluidic outlet in the mixing devicewhich is sealably mated to pipe 101 c.

At this point, the reaction has been completed and the HOCl has beenformed. The production is controlled in-line by measuring pH andconductivity. The pH is used in combination with conductivity based on apre-calibrated relation between the conductivity and concentration ofHOCl measured with spectrophotometry. The measured conductivity is ameasure of the solvent's ability to conduct an electric current.Comparing the same matrix with different known concentrations of HOCland OCl−, a calibration curve (FIG. 8 ) has been established that isused in combination with the pH meter to regulate the titrations andcontrol the process.

Pipe 101 c can be connected to a switch valve 112 that switches betweena waste line 113 and a product collection line 114. Shown in FIGS. 5 and6 . The valve 112 includes the pH meter and the conductivity measuringdevice. These devices measure the concentration (ppm), purity, and pH ofthe HOCl being produced and provide feedback for altering suchproperties of the produced HOCl. Once the HOCl being produced in pipe101 c meets the required concentration, purity, and pH, the valve 112switches from the waste line 113 to the product collection line 114 tocollect the desired product.

The HOCl that has been produced in an air-free manner is collected andbottled in an air-free manner. Placing liquids into a bottle in anair-free manner is known in the art. An exemplary method includesplacing an inflatable vessel (such as a balloon) into a bottle. Theinflatable vessel is connected directly to the collection line 114 andthe HOCl is pumped directed into the inflatable vessel in the bottlewithout ever being exposed to air. Another method involves filling thebottles under vacuum. Another air-free filling method involves fillingthe bottles in an environment of an inert gas that does not interactwith the HOCl, such as an argon environment.

The produced hypochlorous acid is air-free and will have a pH from about4.5 to about 7.5. However, the pH of the produced HOCl can be adjustedpost production process by adding either acid (e.g., HCl) or alkali(e.g., NaOCl) to the produced hypochlorous acid. For example, a pH ofbetween about 4.5 and about 7 is particularly suitable for theapplication of reprocessing heat sensitive medical instruments. Otherapplications, such as its use in non-medical environments, for exampleas in the processing of poultry and fish and general agricultural andpetrochemical uses, the breaking down of bacterial biofilm and watertreatment, may demand different pH levels.

The process can be performed manually or in an automated manner. Fluidicsystems described herein can be operably connected to a computer thatcontrols the production process. The computer may be a PCL-logiccontroller system. The computer opens and closes the valves for thewater inlet, the waste water outlet, and the product outlet according tothe feedback received from the sensors in the system (e.g.,conductivity, pH, and concentration of product (ppm) being produced).The computer can also store the values for the water pressures and wateramounts and can adjust these according to the feedback received from thesensors regarding the properties of the HOCl being produced. Thecomputer can also control the infusion pumps that inject the reagentsinto the water for the production process.

The process can be performed iteratively in that pipe 101 c can beattached to a second fluidic system and the produced HOCl is then flowedthrough the second system where the process described above is repeatedwith the starting solution being HOCl instead of water. In this manner,an increased yield of HOCl is produced. Any number of fluidic systemsmay be interconnected with methods of the invention.

FIG. 7 is a schematic showing another exemplary system 200 for producinghypochlorous acid according to methods of the invention. System 200 isconfigured for regulation of the pH of the incoming water and injectingbuffer for stability. In system 200, water is introduced into pipe 201a. Pipe 201 a has a pH meter 208 connected to it. pH meter 208 measuresthe pH of the incoming water. The pH meter 208 is connected to injectionport 202. The injection port 202 allows for the introduction of at leastone buffering agent to the incoming water. The buffering agent isintroduced by an infusion pump that is sealably connected to port 202.In this manner, the flow rate, and thus the amount, of buffering agentintroduced to the water at any given time is controlled. The infusionpump can be controlled automatically or manually. The rate ofintroduction of the buffering agent to the water is based upon theincoming water quality (conductivity and pH level), the buffercomposition, and the pressure and the flow of the incoming water. Theintroducing can be a continuous infusion or in an intermittent manner.Since the water is flowing through the pipe 201 a in a turbulent manner,there is an initial mixing of the buffering agent with the water uponintroduction of the buffering to the water. This initial mixing may besufficient to properly adjust the properties of the incoming water.

In certain embodiments, further mixing of the water and buffer isperformed prior to conducting the process of producing the HOCl. Inthose embodiments, further mixing occurs when the water with bufferingagent enters the first mixing device 203. Mixing device 203 includes allof the features discussed above with respect to mixing device 102.Mixing device 203 may be configured the same or differently than mixingdevice 102, e.g., same or different number of sub-chambers, same ordifferent diameter of apertures, same or different sizes ofsub-chambers, etc. However, like mixing device 102, mixing device 203 isconfigured to produce a fluidic vortex within each sub-chamber.

The solution enters mixing device 203 through an inlet in the device,which is sealably mated with pipe 201 a. The solution enters the mixingchamber and turbulent mixing occurs in each sub-chambers of the mixingdevice as the solution pass through members in the chamber via theapertures in each member. After mixing in the final sub-chamber, thewater exits the chamber via the fluidic outlet in the mixing devicewhich is sealably mated to pipe 202 b. The water has a pH of at leastabout 8.0, preferably 8.4, and a buffering capacity of pH 5.5-9.0.

The process is now conducted as described above for producing HOCl. Thecompound that generates the proton is next introduced to the water thatis flowing through pipe 201 b via injection port 204. The compound thatgenerates the proton is introduced by an infusion pump that is sealablyconnected to port 204. In this manner, the flow rate, and thus theamount, of compound that generates the proton introduced to the water atany given time is controlled. The infusion pump can be controlledautomatically or manually. The rate of introduction of the compound thatgenerates the proton to the water is based upon properties of the water(conductivity and pH level), the buffer composition, and the pressureand the flow of the water. In certain embodiments, the pump isconfigured to introduce from about 6.5 liters per hour to about 12liters per hour of compound that generates the proton into the water.The introducing can be a continuous infusion or in an intermittentmanner. Since the water is flowing though the pipes in a turbulentmanner, there is an initial mixing of the compound that generates theproton with the water upon introduction of the hydrochloric acid to thewater.

Further mixing occurs when the solution enters the second mixing device205. Mixing device 205 includes all of the features discussed above withrespect to mixing device 102. Mixing device 205 may be configured thesame or differently than mixing device 203, e.g., same or differentnumber of sub-chambers, same or different diameter of apertures, same ordifferent sizes of sub-chambers, etc. However, like mixing device 203,mixing device 205 is configured to produce a fluidic vortex within eachsub-chamber.

The solution enters mixing device 205 through an inlet in the device,which is sealably mated with pipe 201 b. The solution enters the mixingchamber and turbulent mixing occurs in each sub-chambers of the mixingdevice as the solution pass through members in the chamber via theapertures in each member. After mixing in the final sub-chamber, thewater exits the chamber via the fluidic outlet in the mixing devicewhich is sealably mated to pipe 201 c.

The compound that generates the hypochlorite anion is next introduced tothe solution that is flowing through pipe 201 c via injection port 206.The compound that generates the hypochlorite anion is introduced by aninfusion pump that is sealably connected to port 206. In this manner,the flow rate, and thus the amount, of compound that generates thehypochlorite anion introduced to the water at any given time iscontrolled. The infusion pump can be controlled automatically ormanually. The rate of introduction of the compound that generates thehypochlorite anion to the water is based upon properties of the solution(conductivity and pH level) and the pressure and the flow of thesolution. In certain embodiments, the pump is configured to introduceabout 6.5-12 liters per hour of compound that generates the hypochloriteanion into the solution. The amount introduced depends on the desiredconcentration of HOCl (ppm) and flow of water through the pipes. Theintroducing can be a continuous infusion or in an intermittent manner.Since the solution is flowing though the pipes in a turbulent manner,there is an initial mixing of the compound that generates thehypochlorite anion with the solution upon introduction of the compoundthat generates the hypochlorite anion to the solution.

Further mixing occurs when the solution enters the second mixing device207. Mixing device 207 includes all of the features discussed above withrespect to mixing device 102. Mixing device 207 may be configured thesame or differently than mixing devices 205 or 203, e.g., same ordifferent number of sub-chambers, same or different diameter ofapertures, same or different sizes of sub-chambers, etc. However, likemixing devices 205 and 203, mixing device 207 is configured to produce afluidic vortex within each sub-chamber.

The solution enters mixing device 207 through an inlet in the device,which is sealably mated with pipe 201 c. The solution enters the mixingchamber and turbulent mixing occurs in each sub-chambers of the mixingdevice as the solution pass through members in the chamber via theapertures in each member. After mixing in the final sub-chamber, thewater exits the chamber via the fluidic outlet in the mixing devicewhich is sealably mated to pipe 201 d.

At this point, the reaction has been completed and the HOCl has beenformed. The produced HOCl can be measured and collected as describedabove. Pipe 201 d can be connected to a switch valve that switchesbetween a waste line and a product collection line. The valve includes apH meter and a conductivity measuring device. These devices measure theconcentration, purity, and pH of the HOCl being produced and providefeedback for altering such properties of the produced HOCl. Once theHOCl being produced in pipe 201 d meets the required concentration,purity, and pH, the valve switches from the waste line to the productcollection line to collect the desired product.

In another embodiment, a deionizer is placed in-line with incomingwater. The deionizer deionizes the water and then a buffering agent isadded to the deionized water. The production process is then conductedas described for embodiments of system 200 to produce water having a pHof at least about 8, for example 8.4, and a buffering capacity of pH6-8.

The HOCl produced by the above process can be used in numerous differentapplications, for example medical, foodservice, food retail,agricultural, wound care, laboratory, hospitality, dental,delignification, or floral industries.

INCORPORATION BY REFERENCE

Any and all references and citations to other documents, such aspatents, patent applications, patent publications, journals, books,papers, web contents, that have been made throughout this disclosure arehereby incorporated herein by reference in their entirety for allpurposes.

EQUIVALENTS

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativerather than limiting on the invention described herein.

EXAMPLES Example 1 Product Analysis

When spectrophotometry is expanded to also cover the visible range it ispossible to detect colors. The gases generally produced duringproduction of HOCl are ClO₂, Cl₂O and Cl₂, all of which are detectablein the visible range as yellow or yellow-red. Tzanavaras et al. (CentralEuropean J. of Chemistry, 2007, 5(1)1-12). Data in FIG. 9 illustratesthat the HOCl produced by methods on the invention shows no absorptionfrom colored gases as shown by the lack of colored substance. It isknown that HOCl produces a peak at 292 nm (Feng et al. 2007, J. Environ.Eng. Sci. 6, 277-284).

Example 2

HOCl produced by the process described above was stored under heatstress at 40° C. in order to accelerate degradation using four differenttypes of aqueous solutions: (1) reagent grade water (deionized water);(2) tap water; (3) reagent grade water with a phosphate buffer; and (4)tap water with a phosphate buffer. Characteristics of the HOCl productwere monitored after the initial reaction (T=0); four weeks (T=4); eightweeks (T=8); and twelve weeks (T=12).

FIG. 10 is a graph showing the amount (parts per million (ppm)) of HOClinitially produced (T=0) and its stability over time. The data show thatthe reagent grade water (deionized water) without phosphate buffer isthe most stable over the twelve weeks, showing the least amount ofproduct degradation from the initial amount produced. The deionizedwater produces a much more stable product than that produced using tapwater. Additionally, and surprisingly, the data show that phosphatebuffer may negatively impact amount of HOCl product produced.

FIG. 11 is a graph showing how the pH of the HOCl product changed overtime. In all cases, the pH decreased over time, however, for all cases,the pH stayed in the range of pH=4 to pH=7 over the twelve weeks.

FIG. 12 is a graph showing the oxidation capacity of the HOCl productover time. The data show that the product retained oxidation capacityover the twelve weeks regardless of the starting water.

Example 3 Acetic Acid Compared to Hydrochloric Acid

Using the above described process, HOCl was produced using hydrochloricacid (HCl) and acetic acid and thereafter stored under heat stress at 40C. The amount of HOCl initially produced was recorded (T=0) and then theamount of HOCl product remaining after twelve days was recorded. Threebatches of each were produced. The data for the HCl produced HOCl isshown in Table 1. The data for the acetic acid produced HOCl is shown inTable 2.

TABLE 1 HOCl produced with HCl Amount Initial after Batch amount Initial12 days pH after Amount of Amount number (ppm) pH (ppm) 12 daysdegradation pH change 1 192 7.12 159 5.71 17.2% 19.8% 2 183 5.88 1474.01 19.7% 31.8% 3 189 5.21 154 3.97 18.5% 23.8%

TABLE 2 HOCl produced with acetic acid Amount Initial after Batch amountInitial 12 days pH after Amount of Amount number (ppm) pH (ppm) 12 daysdegradation pH change 1 205 4.62 180 4.50 12.4% 2.7% 2 205 5.33 178 5.0413.3% 5.4% 3 207 4.07 178 3.89 13.9% 4.6%

The data show that using acetic acid provides greater product stability,most likely due to greater stability in the pH. Without being limited byany particular theory or mechanism of action, it is believed that thedifferent protonation capacity of acetic acid as compared tohydrochloric acid, i.e., acetic acid donates fewer protons to a liquidthan hydrochloric acid, results in greater HOCl stability over time.

What is claimed is:
 1. A method of producing hypochlorous acid (HOCl),the method comprising the steps of: mixing together in an air-freeenvironment, a compound that generates a proton (H⁺) in water and acompound that generates a hypochlorite anion (OCl⁻) in water, thereby toproduce air-free hypochlorous acid, wherein the compound that generatesthe proton and the compound that generates the hypochlorite anion areintroduced to the water sequentially.
 2. The method according to claim1, wherein the compound that generates the proton is introduced to thewater first and the compound that generates the hypochlorite anion isintroduced to the water second.
 3. The method according to claim 1,wherein the compound that generates the hypochlorite anion proton isintroduced to the water first and the compound that generates the protonis introduced to the water second.
 4. The method according to claim 3,wherein an initial pH of the water is increased prior to addition of thecompound that generates the proton.
 5. The method according to claim 4,wherein the mixing is turbulent mixing.
 6. The method according to claim5, wherein the compound that generates the proton is introduced to thewater and turbulently mixed with the water prior to the introduction tothe water of the compound that generates the hypochlorite anion.
 7. Themethod according to claim 6, wherein the compound that generates thehypochlorite anion is introduced to the water after the compound thatgenerates the proton has been turbulently mixed with the water, andafter introduction, the compound that generates the hypochlorite anionis turbulently mixed with the water.
 8. The method according to claim 1,wherein the compound that generates the proton is selected from thegroup consisting of acetic acid and HCl and wherein the compound thatgenerates the hypochlorite anion is selected from the group consistingof sodium hypochlorite (NaOCl), Mg(OCl)₂ and Ca(OCl)₂.
 9. The methodaccording to claim 1, wherein the water has a buffering capacity fromabout pH 3.5 to about pH 9.0, and wherein the water is purified water towhich at least one buffering agent has been added, wherein the bufferingagent selected from the group consisting of acetic buffer and phosphatebuffer.
 10. The method according to claim 1, wherein the water isflowing through a pipe and has a pressure of at least about 0.5 bar. 11.The method according to claim 1, wherein no more than about 0.6 mLamount of compound that generates the proton is introduced to the flowof water at a single point in time.
 12. The method according to claim 1,wherein no more than about 0.6 mL amount of the compound that generatesthe hypochlorite anion (OCl⁻) is introduced to the flow of water at asingle point in time.
 13. The method according to claim 1, wherein themethod is performed without use of chlorine gas or use of electrolysis.14. The method according to claim 1, wherein a plurality of mixes areiteratively performed.
 15. A method of producing a hypochlorous acid(HOCl) composition, the method comprising: introducing hydrochloric acid(HCl) to a flow of water; turbulently mixing the HCl with the flowingwater in a first mixing device; introducing sodium hypochlorite (NaOCl)to the water after the water has exited the first mixing device; andturbulently mixing the NaOCl with the flowing water in a second mixingdevice, thereby producing hypochlorous acid (HOCl), wherein the methodis performed in an air-free environment and under pressure.
 16. Themethod according to claim 15, wherein the composition is substantiallyfree of chlorine gas.
 18. The method according to claim 15, wherein thecomposition comprises a pH from about 4.5 to about 7.5.
 19. The methodaccording to claim 18, wherein the composition comprises a pH from about6.0 to about 7.0.
 20. The method according to claim 15, wherein the HOClcomprises a concentration of at least about 200 ppm.